1. Technical Field
The present invention relates to a substrate plating apparatus, and particularly to a substrate plating apparatus for filling grooves for wiring formed in a semiconductor wafer with copper or another metal.
2. Description of the Related Art
Conventionally, wiring has been formed in a semiconductor wafer by first depositing a conductive layer on a wafer surface using sputtering or a similar technique. Next, unnecessary portions of the conductive layer are removed through a chemical dry etching process using a pattern mask formed of resist or the like.
In conventional processes, aluminum (Al) or an aluminum alloy has been used form the wiring. However, wiring has been made thinner to keep up with increased complexity of semiconductor devices. Increasing current density generates increased thermal stress and higher temperatures. This leads further to stress-migration or electro-migration that gives rise to such disorders as wiring breakage or short-circuiting.
To avoid an excessive generation of heat by current in the wiring, a metal having a higher conductivity such as copper must be used to form the wiring. However, it is difficult to perform dry etching on copper or a copper alloy that has been deposited over an entire surface as in the process described above. An alternative process would be to first form grooves for the wiring according to a predetermined pattern and then fill the grooves with copper or a copper alloy. This method eliminates the process of removing unnecessary parts of the conductive layer by etching, requiring only that the surface of the wafer be polished to remove uneven areas. The method has an additional benefit of being able to simultaneously form connecting areas called plugs that connect an upper layer and a lower layer of multi-layer wiring.
However, the shape of these wiring grooves and plugs have a considerably high aspect ratio (the ratio of depth to diameter or width) as the width of the wiring becomes smaller, making it difficult to fill the grooves with an even layer of metal using sputtering deposition. A chemical vapor deposition method (CVD) has been used for depositing various materials, but it is difficult to prepare an appropriate gas employing copper or a copper alloy. Further, when using an organic material, carbon (C) from the material becomes mixed with the deposition layer and increases a tendency toward migration.
Therefore, a method was proposed for performing electroless or electrolytic plating by immersing a substrate into a plating solution. With this method, it is possible to fill wire grooves having a high aspect ratio with a uniform layer of metal. However, when performing steps of this plating process consecutively in the same apparatus that must maintain a clean atmosphere, chemicals used in a preprocess and plating process become chemical mist and gas that are dispersed throughout the apparatus. The chemical mist and gas are thought to deposit on the substrate after a post-plating processes. This problem exists even when chemicals used in the preprocess and plating process are hermetically sealed in a process bath because the seal on the process bath must be broken to insert and remove wafers. Therefore, it is not possible to prevent the chemical mist and gas from dispersing throughout the apparatus with this construction.
In view of the foregoing, it is an object of the present invention to provide a substrate plating apparatus capable of performing continuous plating operations within one apparatus without wafers becoming contaminated, after a post-plating processes, by chemicals used in a plating process and the like.
It is another object of the present invention to provide a substrate plating apparatus capable of forming a plating film of uniform thickness on a plating surface of a wafer, while encouraging bubbles to escape from fine holes or grooves in the plating surface and deterring particles from being deposited on the plated surface.
It is yet another object of the present invention to provide a substrate plating apparatus capable of automatically analyzing composition of a plating solution from time to time and quickly displaying results of the analysis on a monitor.
According to an aspect of the present invention, there is provided a substrate plating apparatus for continuously performing a plating process and a post-plating process within the same apparatus. The substrate plating apparatus comprises a contaminated zone within which the plating process is performed, a clean zone within which the post-plating process is performed, and a partition dividing the apparatus into the contaminated zone and the clean zone, wherein each zone is independently ventilated.
With this construction, the apparatus is partitioned into a contaminated zone in which chemical mist and vapor from chemicals used in the plating process are dispersed, and a clean zone in which a clean atmosphere is required. Each zone has an independent method for treating particles. Accordingly, the invention can prevent the chemical mist and vapor from being deposited on the substrate after completion of the post-process.
According to another aspect of the present invention, the partition is provided with a shutter that can be opened and closed. Hence, the substrate can be transferred between the contaminated zone and clean zone before conducting a preprocess, or after conducting the plating process, by opening the shutter provided in the partition.
According to another aspect of the present invention, air flow in the contaminated zone comprises a circulating flow circulating therein, and a supplied and discharged flow which is supplied externally into the contaminated zone and is discharged externally. The circulating flow flows downwardly as clean air from a ceiling of the apparatus through the contaminated zone and, after a scrubber and/or mist separator remove chemical mist or vapor of solution from the circulating flow, cycles back into the contaminated zone from the ceiling of the apparatus as clean air.
With this construction, a sufficient amount of clean air can be supplied to the contaminated zone, and particles can be prevented from contaminating a processed substrate while minimizing an amount of air flow that is supplied from an external source and exhausted.
According to another aspect of the present invention, the substrate plating apparatus further comprises conveying devices provided one in each of the clean and contaminated zones for conveying a substrate through the zones. Each conveying device has a hand portion for retaining the substrate, and a coarse washing chamber is disposed adjacent to the partition for coarsely washing the substrate while being retained by the hand portion of the conveying device provided in the contaminated zone after the plating process has been completed.
With this construction, the hand portion of the conveying device provided in the contaminated zone is washed along with the processed substrate. Hence, the invention can prevent contaminants from the plating solution deposited on the hand portion from being transferred onto the conveying device in the clean zone.
According to another aspect of the present invention, a method for plating a substrate by continuously performing a plating process and a post-plating process within the same apparatus, comprises: partitioning an inside of the plating apparatus with a partition to form a contaminated zone and a clean zone, with each zone being independently ventilated; disposing a conveying device in each of the clean and contaminated zones for conveying a substrate through the zones; disposing a coarse washing chamber adjacent to the partition; and coarsely washing the substrate while the same is retained by a hand portion of the conveying device disposed in the contaminated zone.
With this method, the hand portion of the conveying device disposed in the contaminated zone is washed along with the processed substrate. Hence, it is possible to remove plating solution deposited on the hand portion and prevent chemical mist and vapor from being introduced into the clean zone.
According to another aspect of the present invention, the method for plating a substrate further comprises the steps of withdrawing the hand of the conveying device after the coarse washing process is completed, coarsely washing the substrate again by itself, and subsequently conveying the substrate into the clean zone. With this method, it is possible to more effectively prevent chemical mist and vapor from being introduced into the clean zone.
According to another aspect of the present invention, a substrate plating apparatus for plating a surface of a substrate with a plating solution comprises a plating bath that is hermetically sealed and accommodates the substrate to be plated, and a flow path of the plating solution is formed to be parallel to the surface of the substrate. Since the plating solution flows parallel to the substrate surface, a more uniform plating layer can be formed on the surface of the substrate.
According to another aspect of the present invention, a substrate is maintained such that its surface is slanted in relation to a vertical plane. This construction prevents particles from depositing on a surface of a plated substrate.
According to another aspect of the present invention, the substrate plating apparatus further comprises a retaining device for retaining a substrate such that its surface is slanted from a vertical plane within a range of 30 degrees from vertical while a plating process is performed. With this construction, air bubbles can be easily dislodged from fine holes formed in the surface and plating solution can flow into the fine holes to form a plating layer on interior surfaces of the fine holes. Further, particles do not become deposited on the surface of the substrate.
According to another aspect of the present invention, a method for plating a surface of a substrate with a plating solution, comprises: disposing a substrate to be plated within a hermetically sealed plating bath; introducing plating solution into the plating bath; and plating the surface of the substrate while varying pressure of the plating solution and changing direction of the flow of the plating solution. With this method, a dense plating layer can be formed in fine grooves formed in the substrate surface.
According to another aspect of the present invention, plating solution flows parallel in relation to a surface of a substrate, and a width and length of a flow path of the plating solution are larger than a diameter of the substrate. Since the plating solution flows parallel to the surface of the substrate, a plating layer of uniform thickness can be formed on the surface.
According to another aspect of the present invention, a plating bath comprises a main section having an open area, a side plate capable of opening or closing to expose or cover the open area in the main section, a retaining mechanism for retaining a substrate on the side plate, and an annular packing disposed around the open area of the main section. The surface on an edge of the substrate mounted on the side plate contacts the packing when the open area of the main section is covered by the side plate, and a flow path of the plating solution is formed to be parallel to a surface of the substrate between the main section of the plating bath and the substrate.
With this construction, an inner edge of the annular packing protrudes in a funnel shape externally from the main section, and is pressed inwardly by contact from a periphery of the substrate. Accordingly, by setting pressure in the plating bath higher than that external to the plating bath, the packing presses firmly against the periphery of the substrate to increase a sealing effect.
According to another aspect of the present invention, an inner peripheral edge of the annular packing protrudes externally of the main section of the plating bath in a funnel shape and contacts a surface on the periphery of the substrate, and internal pressure in the plating bath generates a force on the packing for increasing sealing performance between the packing and the substrate.
According to another aspect of the present invention, the substrate plating apparatus further comprises a sensor for detecting whether a substrate is mounted on the side plate, whereby supply of plating solution to the plating bath is halted when the substrate is detected not to be mounted on the side plate based on output from the sensor.
Accordingly, by providing a sensor to detect existence of a substrate, and a device for stopping supply of plating solution to the plating bath when output from the sensor indicates that a substrate is not mounted in the apparatus, there is no danger of plating solution being supplied before an airtight space is formed between the main section of the plating bath and the substrate for supplying plating solution. As a result, plating solution will not leak out of the apparatus.
According to another aspect of the present invention, the main section of the plating bath further comprises a shielding plate disposed opposite the substrate. The shielding plate has an electric field adjusting hole formed approximately in a central portion of the main section, and an anode is fitted in the electric field adjusting hole such that a surface of the anode is approximately flush with a surface of the shielding plate. With this construction, plating solution can flow between the surfaces of the shielding plate and anode, and a surface of the substrate, with little agitation to enable formation of a uniform plating layer.
According to another aspect of the present invention, a substrate plating apparatus further comprises a sampling device for sampling plating solution at a fixed period, an automatic analyzing device for automatically analyzing components of the sampled plating solution, and a monitoring device for displaying results of analysis performed by the automatic analyzing device.
With this construction, it is possible to sample a plating solution used in a plating process at regular periods throughout the process, automatically analyze components of the samples, and quickly display results of the analysis.
According to another aspect of the present invention, the plating solution is an electrolytic copper plating solution and the automatic analyzing device measures at least one of copper ion concentration, sulfuric acid concentration, chlorine ion concentration, and additive concentration.
According to another aspect of the present invention, the plating solution is an electroless copper plating solution and the automatic analyzing device measures at least one of copper ion concentration, reductant concentration, pH, chelate concentration, dissolved oxygen, dissolved hydrogen, and additive concentration.